fink vs grass up

fink

verb

  • To betray a trust; to inform on. 

noun

  • An informer. 

  • A strikebreaker. 

  • A contemptible person. 

  • Any of several birds in the family Ploceidae native to southern Africa. 

grass up

verb

  • To betray by informing on. 

How often have the words fink and grass up occurred in a corpus of books? (source: Google Ngram Viewer )